<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .z1{

            width: 100px;
            height: 100px;
            background-color: greenyellow;
            border: 5px  solid green;
            border-bottom: 15px dotted plum ;/*可设置单方向边框*/
        }
        .z2{
            width: 100px;
            height: 100px;
            background-color: #ea6d93;
            border-radius: 5px ;/*边框圆角*/
        }
        .z3{
            width: 100px;
            height: 100px;
            background-color: greenyellow;
            border: 5px  solid green;
            padding: 30px;/*内边距*/
        /*    边框和内间距都会使元素变大，外间距不会，其不属于元素*/
            box-sizing: border-box;/*切换盒子模型计算方案为边框盒子，所有内容都是算在预设的宽高之内，靠压缩元素实现*/
        }
    </style>
</head>
<body>
<span></span> <span></span> <span></span>
<div class="fu">
    <div class="z1"></div>
    <div class="z2"></div>
    <div class="z3"></div>
    <div class="z4"></div>
</div>
</body>
</html>